Colour camera devices such as TV cameras, Video cameras and the like incorporate what are essentially three separate colour channels, which separately sense the three primary colours in the object or scene being recorded.
It is well known that the three separate colour channels must be balanced so as to record the object or scene as a faithful reproduction of its actual colours. For this purpose colour reference images have been proposed in the past. Examples are shown in U.S. Pat. Nos. 3,552,288 and 3,572,943.
These earlier devices are intended for aligning colour telecine camera chains to a standard reference colour balance which will be uniform for all cameras.
It is well known however that the appearance, and particularly the colour and hue of objects, persons and scenes being recorded may vary widely depending upon the light falling upon them. Natural outdoor light produces what most persons experience as the most natural colour. However it is known that even natural outdoor light can vary at different times of day. Artificial light produces a different appearance from natural light, and different forms of artificial light or combinations of artificial light and natural light will produce other variations again. As a result, even though the cameras are first aligned to such a standard reference image, when used for recording images subjected to an unusual form of lighting, the end result may appear to be an unbalanced unnatural colouring.